The present invention relates to redundancy switching to enhance the reliability of communications systems, and more particularly to an electromechanical reed switch useful in constructing redundancy switches for satellite communications.
In communications systems, particularly satellite communications systems, it is desirable to provide a number of redundant system elements to be used in the event of a component failure. In order to connect the redundant elements into the system, a highly flexible switching system is required. One type of switch which does provide a high degree of flexibility is known as a "T" switch. The T-switch has four ports and three positions, with any one port being connectable to any of the three remaining ports. A microwave version of a T-switch is disclosed in U.S. Pat. No. 4,201,963, and the switch and its three possible positions are schematically illustrated in FIG. 1. The usefulness of the T-switch can be easily appreciated from the connection diagrams of FIGS. 2(A)-2(D). In these FIGS. 2(A)-2(D), the input terminals are labeled 1-8, while the output terminals are labeled a-l. It is necessary to provide a signal path for each of the 8 inputs, and four additional signal paths are provided for redundancy purposes. If a failure occurs in one of the signal paths being used, the input to that signal path can be easily switched to one of the available redundant paths and the system will remain in operation. The various illustrations of FIGS. 2(A)-2(D) illustrate the worst case of four consecutive signal path failures necessitating substantial rerouting of the input signals.
In communications satellite applications, the high cost per pound of the orbited satellite requires that a maximum number of switchable combinations be available with the fewest possible number of switches, and in this regard the T-switch is particularly advantageous. It is also preferable that the T-switch itself is small and lightweight.
In many instances, switches utilized in satellite communications must be capable of extremely fast switching times and, therefore, solid state switching is a necessity. The requirements of redundancy switches are quite different. Since the redundancy switches need not be constantly changing states at the signal rate but need only function in case of a signal path failure, they can be designed with much lower switching speeds and electromechanical type switches are viable options. However, the operating speeds of currently available electromechanical switches are slower than desirable even for redundancy switching.
The reliability of redundancy switches in satellite communications systems is extremely important, since a failure in the redundancy switching system would be extremely undesirable. Thus, it is important not only that the probability of failure of the redundancy switch in its present state be substantially zero, but it is also important that the probability of failure in an attempt to change the state of the redundancy switch be substantially zero.
Further, since the states of the redundancy switches may not be changed for long periods of time, it is important that the steady state power consumption of the redundancy switch be substantially zero.
Electromechanical T-switches are known, but the reed switching element is typically controlled by a solenoid driver, e.g. a plunger, connected to the reed. Due to the inertia of the driver itself, the switch speeds of such configurations are undesirably slow and power consumption high.
A typical T-switch configuration is shown in FIG. 3 utilizing six bistable reed switches to connect the various ports as shown. Although the configuration of FIG. 3 illustrates the first, second and third ports being arranged at 120 degree intervals around the circumference of a circle with the fourth port being located at substantially the center thereof, it should be realized that other geometrical arrangements may be preferred as long as the interconnections are maintained.
The first switch position illustrated in FIG. 1 can be realized by closing switches 10 and 12, the second switch position of FIG. 1 can be realized by closing switches 14 and 16, and the third switch position of FIG. 1 can be realized by closing switches 18 and 20. When constructing such a T-switch from conventionally available reed switches, the weight of the solenoid actuators can be considerable and, as mentioned above, the inertia of these actuators results in undesirably slow switching speeds.